Why did the metatarsals of birds fuse together?

["Henri R&#1046;nkk&#1046;" <overmind@iobox.fi>]

Dear all,

Why did the metatarsals of birds fuse together? Some time ago, some one (I'm 
sorry, I don't remember the name) posted onto this list that the fusion was an 
adaptation to hopping from branch to branch. I think I didn't get the logit. 
Would it be that the fusion made the tarso-metatarsus part of the limb 
stronger, and so less vulnerable to facture during rapid deceleration occuring 
when the bird "lands" on a branch.

If you have looked into this matter, I'd like to hear from you.

Thanks in advance,
Henri Rönkkö
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Soittoäänet ja ikonit matkapuhelimeen!  http://www.iobox.fi/